Phase Diagrams And Alloying Flashcards
Concept of a phase, solid solubility, binary systems, eutectic and eutectoid alloy systems.
Do materials all have one example of each phase?
No. For example, Iron is polymorphic, carbon can be diamond or graphite, sugar can be crystals or candy.
What are the two kinds of solid solutions?
Split this into multiple cards.
Interstitial. Which is a parent structure “Solvent” with much smaller “Solute” atoms in the gaps of the structure. There is also a limit on how many solute atoms into the structure (there is a solubility limit).
Substitutional. Which is a crystal structure with some of the atoms of one element replaced by atoms of a different element. This can be done, until all atoms are eventually replaced. The atoms must be of a similar size, and the elements must have the same crystal structure. Can have unlimited solubility.
What causes the solubility limit to change?
Temperature.
Define a phase?
A component within a system that has uniform physical characteristics.
Solid phase is also called?
Alpha.
What is the phase diagram of an alloy with complete solid solubility called?
Binary Isomorphous Phase Diagram.
For any non-100% composition of Alpha, the material will melt at what temperature?
Across a range of materials between the melting temperature of both materials.
What is the upper line of the range of melting temperatures on a Binary Isomorphous Phase Diagram called?
Liquidus.
What is the lower line of the range of melting temperatures on a Binary Isomorphous Phase Diagram called?
Solidus.
What is an “Interstitial” solid solution?
An interstitial solid solution is a parent structure “Solvent” with much smaller “Solute” atoms in the gaps of the structure. There is a limit on how many solute atoms into the structure (this is referred to as a solubility limit).
What is a “Substitutional” solid solution?
A substitutional solid solution is a crystal structure with some of the atoms of one element replaced by atoms of a different element. This can be done until all atoms are eventually replaced. The atoms must be of a similar size, and the elements must have the same crystal structure. Can have unlimited solubility.
What is a “Eutectic” composition?
The eutectic composition of certain alloys is the composition at which the entire alloy melts at a single temperature.
True/False: The temperature at which an alloy with a eutectic composition melts at is higher than the melting temperature of either pure materials.
False. The melting temperature is actually lower than the melting temperature of either pure metal. The word Eutectic means easily melted.
In a phase diagram what is the “Solvus” line?
The solvus line describes the point at which a material changes from a single solid phase to two solid phases.
What is a “Eutectic Reaction”?
A eutectic reaction is the moment at which a single liquid phase transforms into two solid phases at once. This has a unique structure.
What kind of solid solution is Steel?
Interstitial. Carbon atoms are much smaller than iron atoms so they are able to sit in the interstitial spaces of the iron crystal lattice.
What percentage of carbon can steel contain?
Anywhere from 0.02% to 1.7% carbon. Anything above 1.7% is no longer considered steel, it is instead known as Cast Iron.
How much carbon can Gamma Iron/Austenite contain?
Gamma Iron/Austenite can accommodate up to 1.7% carbon.
What temperature can Gamma Iron/Austenite exist at?
Temperatures above 723*C.
What crystal structure is Gamma Iron/Austenite?
FCC.
How much carbon can Alpha Iron/Ferrite contain?
Alpha Iron/Ferrite can accommodate up to 0.02% carbon.
What temperature can Alpha Iron/Ferrite exist at?
Between room temperature and 910*C.
What crystal structure is Alpha Iron/Ferrite?
BCC.
What is the other name for Cementite?
Iron Carbide.
What is the other name for Gamma Iron?
Austenite.
What is the other name for Alpha Iron?
Ferrite.
True/False: Cementite is not a solid solution.
True.
What composition is Iron Carbide?
6.67% Carbon. Single Solid Phase.
What is the solubility limit of Carbon in FCC Iron?
1.7%.
What is the solubility limit of Carbon in BCC Iron?
0.02%
What is the Eutectoid point of steel?
The point at which solid Gamma Iron turns into both Alpha Iron and Cementite.
What is the Eutectoid composition of steel?
0.8% Carbon.
At what temperature does the Eutectoid reaction occur for steel?
723*C.
True/False: The Eutectoid and Eutectic structures are considered a phase.
False. They are considered combinations of two phases.
What is the alternate name for the Eutectoid Solid steel?
Pearlite.
